Any best practices or examples of mix and match functionality on a fashion e-commerce?

I'm trying to design this feature, but so far not much luck finding any decent implementations of this feature. one example is http://www.bonarium.com but even that is pretty basic.

what would the user flow be like? for now i think the feature could be triggered when a user add an item to cart and then browses to a category that compliments the 1st one (e.g. 1st shirt, 2nd pants)

and which pages would this feature be able to be accessed from. catalog? pdv? cart?

how would the user be able to add products into selection of products?